(1) Due to its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.

(1) During the Middle Ages, an amulet of Opal, or one that contained Opals mixed with other gems, protected its wearer against faulty vision, while strengthening the mind and memory.

(2) Opal was considered to be a talisman that would allow its owner to recognize his friends and enemies. In the presence of an enemy, the Opal would grow pale, but in the presence of friends or allies it would turn red with pleasure.

(1) Opal is the national gemstone of Australia, probably because 97% of the world's supply comes from there.

Following the publication of Sir Walter Scott's Anne of Geierstein in 1829, opal got a bad rep. In the novel, the Baroness of Arnheim wears an opal talisman with supernatural powers. When a drop of holy water falls on the talisman, the opal turns into a colorless stone and the Baroness dies soon thereafter. Due to the popularity of Scott's novel, people began to associate opals with bad luck and death. Within a year of the publishing of Scott's novel in April 1829, the sale of opals in Europe dropped by 50%, and remained low for the next 20 years or so.